The invention relates to a device and a method for measuring panes, more particularly windshields of vehicles. The device comprises a light source and a light sensor, which are arranged in such a way that a light beam emanating from the light source passes through the pane and is incident on the light sensor.
If a light beam is incident on a pane under an angle of incidence which includes an angle unequal to 0° with the normal of the pane, there may be internal reflection within the pane, by means of which the light beam is split into a primary beam and a secondary beam. An observer peering onto the light source through the pane sees a double image of the light source. A double image arises, in particular, if the pane is wedge-shaped in the relevant region, i.e. if the two outer faces are not parallel to one another, or if the pane is curved at said location.
By way of example, in the case of windshields of vehicles, such double images are perceived as bothersome if the light of an approaching vehicle is visible in duplicate form in darkness. It is known to measure windshields in respect of the generation of double images. The double image angle, i.e. the angle included between the primary beam and the secondary beam, is of particular interest. To this end, a light beam is guided through the pane onto a light sensor and the size of the distance between the primary beam and the secondary beam on the light sensor is established.
In these measurements, the problem arises that it is not entirely straightforward to measure the primary beam and the secondary beam on a light sensor since the primary beam is regularly many times brighter than the secondary beam.